First row shifting

Hello,

if you look at the table here http://moreyouthfulskin.com/de/smoothie-staerkere-schoene-naegel/ and are scrolling down, you´ll see that the first row is shifting to the right.
I think this is caused by the fact that there is no line under the first row.
Here is the coding I am using:

.tablepress-roster7-table .row-2 td,
.tablepress-roster7-table .row-12 td,
.tablepress-roster7-table .row-17 td {
background-color: #12c9c4 !important;
}

.tablepress-roster7-table .row-3 td,
.tablepress-roster7-table .row-4 td,
.tablepress-roster7-table .row-5 td,
.tablepress-roster7-table .row-6 td,
.tablepress-roster7-table .row-7 td,
.tablepress-roster7-table .row-8 td,
.tablepress-roster7-table .row-9 td,
.tablepress-roster7-table .row-10 td,
.tablepress-roster7-table .row-11 td,
.tablepress-roster7-table .row-13 td,
.tablepress-roster7-table .row-14 td,
.tablepress-roster7-table .row-15 td,
.tablepress-roster7-table .row-16 td,
.tablepress-roster7-table .row-18 td {
font-weight: bold;
background-color: #71f2ed !important;
}

.tablepress-roster7-table th,
.tablepress-roster7-table td {
font-family: Cambria;
font-size: 14px;
font-weight: bold;
text-align: center;
}

.tablepress-roster7-table th,
.tablepress-roster7-table td {
width: 50%;
margin: 0 auto 1em;
}

How do I add a line (frame) under the first row to prevent its shifting to the right?
Thank you,

Milada

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