Tab box border widens with addition of tabs

I'm working on a digital ad reporting dashboard:

https://branddeliver.com/four/

The problem I'm having is that every time I add a new tab, the border of the container gets wider (see image below...red arrows point to the border).

I had to add custom CSS to format the tables--and that may be the culprit. If not, is this something I can somehow get rid of totally? I want much thinner lines if possible. I'll include the custom css I added beneath the image. Thank you for your help...

/* Add to Brizy Global CSS or a Custom HTML block */
@import url('https://fonts.googleapis.com/css2?family=Poppins:wght@400;600&family=Montserrat:wght@400;900&display=swap');

.gsheet-container {
    font-family: 'Poppins', sans-serif;
    color: #333;
    background-color: #f8f9fa;
    padding: 20px;
}

.gsheet-inner-container {
    width: 100%;
    max-width: 900px;
    background: white;
    padding: 25px;
    border-radius: 12px;
    box-shadow: 0 6px 12px rgba(0,0,0,0.1);
    margin: 0 auto;
}

.gsheet-last-updated {
    font-size: 1.2em;
    text-align: center;
    margin-bottom: 20px;
    color: #007bff;
    font-weight: 600;
}

.gsheet-download-btn {
    display: inline-block;
    margin-bottom: 15px;
    padding: 10px 20px;
    background: #28a745;
    color: white;
    border: none;
    border-radius: 6px;
    cursor: pointer;
    font-size: 1em;
    font-weight: 600;
    transition: background 0.3s ease;
}

.gsheet-download-btn:hover {
    background: #218838;
}

.gsheet-summary-cards {
    display: flex;
    gap: 15px;
    margin-bottom: 20px;
    flex-wrap: wrap;
}

.gsheet-summary-card {
    flex: 1;
    background: linear-gradient(135deg, #007bff, #0056b3);
    color: white;
    padding: 15px;
    border-radius: 8px;
    text-align: center;
    min-width: 150px;
}

.gsheet-summary-card h3 {
    font-family: 'Montserrat', sans-serif;
    margin: 0;
    font-size: 1.1em;
    font-weight: 400;
    color: white;
}

.gsheet-summary-card p {
    font-family: 'Montserrat', sans-serif;
    margin: 5px 0 0;
    font-size: 1.4em;
    font-weight: 900;
}

.gsheet-table {
    width: 100%;
    border-collapse: collapse;
    color: #444;
}

.gsheet-table th, .gsheet-table td {
    padding: 8px 16px; /* Reduced vertical padding from 14px to 8px */
    border-bottom: 1px solid #e0e0e0;
}

.gsheet-table thead th {
    background: linear-gradient(135deg, #007bff, #0056b3);
    color: white;
    font-weight: 600;
    cursor: pointer;
}

.gsheet-table th:nth-child(n+2), .gsheet-table td:nth-child(n+2) {
    text-align: right;
}

.gsheet-table tbody tr:nth-child(even) {
    background-color: #f6faff;
}

.gsheet-table tbody tr {
    transition: transform 0.2s ease, background-color 0.3s ease;
}

.gsheet-table tbody tr:hover {
    background-color: #e6f0fa;
    transform: translateY(-2px);
}

.gsheet-table tfoot tr {
    font-weight: 600;
    background-color: #e9ecef;
    border-top: 2px solid #ccc;
}

.gsheet-loading-message {
    text-align: center;
    padding: 20px;
}

@media (max-width: 600px) {
    .gsheet-table, .gsheet-table thead, .gsheet-table tbody, .gsheet-table th, .gsheet-table td, .gsheet-table tr {
        display: block;
    }

    .gsheet-table thead tr {
        position: absolute;
        top: -9999px;
        left: -9999px;
    }

    .gsheet-table tr {
        border: 1px solid #ddd;
        margin-bottom: 5px; /* Reduced from 10px to 5px */
        border-radius: 8px;
        background: white;
        box-shadow: 0 2px 4px rgba(0,0,0,0.1);
    }

    .gsheet-table td {
        border: none;
        border-bottom: 1px solid #eee;
        position: relative;
        padding: 8px 16px; /* Match desktop padding, reduced from 14px */
        text-align: right;
        font-size: 0.9em;
    }

    .gsheet-table td:last-child {
        border-bottom: 0;
    }

    .gsheet-table td::before {
        content: attr(data-label);
        position: absolute;
        left: 15px;
        width: 45%;
        padding-right: 10px;
        font-weight: 600;
        text-align: left;
        color: #007bff;
    }

    .gsheet-summary-cards {
        flex-direction: column;
    }

    .gsheet-download-btn {
        width: 100%;
        text-align: center;
    }
}